External Airbag Protects Pedestrians

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External Airbag Protects Pedestrians

Researchers at Cranfield University in England have developed an external airbag they say will significantly reduce pedestrian fatalities and injuries in the event of a crash.

The system deploys a hood - or bonnet, as the British call it - airbag at the base of the windshield, which research shows is where a pedestrian's head is most likely to hit. The system uses radar and infrared technology to "pre-detect" a collision and inflates quickly enough to cushion the impact, said Roger Hardy of the university's Cranfield Impact Centre.

"Test results indicate that the system works extremely well," Hardy said of the system, which was tested on a Fiat Stilo. "When fitted to a demonstrator vehicle not originally designed with pedestrian protection in mind, the results were well inside all current legal criteria for pedestrian protection currently in force in Europe."

The bonnet airbag is shaped like a "U" to preserve the driver's visibility while protecting the pedestrian from the lower half of the A pillars - what the lay person might call the windshield frame. The researchers focused on the A pillars because they are the stiffest part of the windshield. The airbag also raises the car' hood several inches - much like the Jag's system - to increase the crush depth, Hardy said. The wider the gap beneath the hood, the softer the impact.

The researchers tested the technology on a Fiat Stilo. A standard car hitting a pedestrian at 25 mph would have a Head Impact Criterion score of about 1,000. That translates to an 18 percent chance of a life-threatening injury. The score falls to between 692 and 945 for Stilo fitted with the Cranfield air bag and falls even further to between 234 and 682 when coupled with the energy-absorbing hood. Engineers at Fiat are experimenting with an "adaptive bumper system" that uses four springs to push the front bumper forward before a collision so it can absorb more energy.

A pyrotechnic device deploys the airbag, so there is no stored air or gas supply on the vehicle. Hardy anticipates production of the system to begin in as little as five years and said it would add little to the cost of the vehicle. Hardy says the question of whether we'll see such technology in the United States depends upon future legislation and a decision by European automakers to include such systems on cars exported to the U.S.

NHTSA spokesman Eric Bolton said he could not comment on the Cranfield University system. But he told Wired.com that pedestrians in Europe are more likely to be involved in car accidents because the streets there are narrower and more crowded than those in the U.S.

Cranfield Impact Center also has developed an energy absorbing windshield mounting system - essentially a Z-shaped metal strip - that mounts between the windshield and the frame (see the inset photo at right). The system increases the flexibility of the windshield, allowing it to absorb more energy in the event of a collision. Cranfield says 30 percent of all pedestrian fatalities involve head injuries.